A number of up-to-date applications, including advanced radars with high single-shot resolution, precise 3-D imaging, laser tomography, time imaging spectroscopy, etc., require low-cost, compact and reliable sources enabling generation of high-power (10-103 W) single optical pulses in the picosecond range, which optical pulses can be produced typically by laser-based light sources such as solid and dye microcavity lasers and semiconductor laser diodes. However, in many cases the use of solid and dye microcavity lasers is limited for applications such as those mentioned above due to their relatively high cost and large dimensions as compared with semiconductor laser diodes.
Producing picosecond high-power pulses with semiconductor laser diodes can be based on various operating modes. In the gain-switching mode, a picosecond optical pulse is achieved due to significant gain overshoot over the optical losses as a result of a sufficiently short leading edge of the pumping current pulse. In the gain-switching mode, optical power of typically ˜0.1 W for a 10×400 μm laser chip can be obtained in a single optical pulse, which fulfils the power requirements in some applications. However, the gain-switching method sets high requirements for the current drivers since the rise time of the current pulse has to be shorter than the characteristic lasing delay. Such current drivers are not commercially available, particularly for high-power laser diodes.
Alternatively, the optical power in a picosecond pulse can be increased drastically, if a Q-switched single-heterostructure laser diode is used. This method provides power as high as 10 W for a 10×400 μm laser chip. However, the operation of the Q-switched single-heterostructure laser diode is very complicated. Thirdly, a well-known method for high-power picosecond pulse generation utilizing diode lasers is the method of ion implantation. Ion implantation can be used for any type of diode laser for the formation of absorbing regions, which operate as an optical shutter. The maximum achievable optical power in the picosecond pulse is of the same magnitude as that obtained with a Q-switched single-heterostructure laser diode. However, the ion implantation techniques available are rather complicated and expensive, and the reliability of the laser diodes is questionable.